I planted Copra and Walla Wallas for the first time this year. I started both from seed. They seem to be doing equally well with good top growth and now starting to bulb. I don't know if the bulbing is "on schedule," but they're both doing it. It's not really an answer to your question about what's common, but as one other data point, they seem pretty comparable in they growth characteristics.

thanks for the response to my posting, ya i guess its such a big difference in their growth characteristics this year that has me puzzled, i dont remember from last year that there was such a difference. The Walla Wallas are visibly bulbing, im sure, or lets say i hope, the Copra are doing the same!